The present invention relates to a reflection mirror which electrically controls reflectivity or transmittivity of light thereof by the use of a liquid crystal.
The reflection mirror may be used as an interior room mirror, exterior side mirror or the like of an automotive vehicle.
In a conventional reflection mirror, chrome has been vapor-deposited on a rear surface of a glass substrate to form a reflection film. Reflectivity of light of the conventional reflection mirror with the chrome film, however, could be increased at most to about 50% even if the chrome film is thickened enough.
It has been suggested to increase the reflectivity of light to as high as 80%-90%, for instance, by the use of aluminum. It was disadvantageous, however, that aluminum film peels off because of insufficient adhesiveness thereof to the glass substrate when aluminum is vapor-deposited directly on the glass substrate.
To overcome the disadvantage, it has been suggested in the Japanese publication, "Journal of Applied Physics, vol. 29, No. 3, page 141", that chromel be used between the glass substrate and the aluminum film to improve adhesiveness of the aluminum film to the glass substrate.
It was still disadvantageous, however, in the following points. (1) Total reflectivity of light cannot be increased sufficiently high even if the aluminum film is formed on the chromel film, since reflectivity and transmittivity of light of chromel is low as chrome is. (2) Chromel cannot be vapor-deposited on a liquid crystal cell since, when chromel is vapor-deposited on a rear surface of the glass substrate used to support the liquid crystal cell in which a pair of transparent electrodes, a pair of orientation film sand a liquid crystal, the orientation of the orientation films is disturbed by the temperature at the vapor-depositing.
The second disadvantage (2) is explained hereinunder in more detail. The reflection mirror using the liquid crystal cell used as a dazzle-free interior room mirror of an automotive vehicle, for instance, is manufactured in general in a series of processes shown in FIG. 8.
Firstly, at a step 100, soda glass is cut in a shape of transparent glass substrate. At a step 102, a transparent conductive film is formed on the glass substrate as an electrode. The transparent conductive films used indium tin oxides in which weight percentage ratio between In.sub.2 O.sub.3 and SnO.sub.2 is 95:5 and are formed to film thickness of 1000 .ANG. by an electron beam under 350.degree. C.-400.degree. C. and oxygen partial pressure of 1.times.10.sup.-2 Pa-5.times.10.sup.-2 Pa. Next, at a step 104, acid-resistant resist ink is printed on the transparent conductive film over a whole range corresponding to a dazzle-free portion so that a masking is provided. At a step 106 thereafter, the substrate with the transparent conductive film is dipped for two minutes under temperature of 45.degree. C. in a fluid solution mixture of concentrated hydrochloric acid and water in 1:1 ratio so that surrounding portions of the transparent conductive film corresponding to a sealing portion is removed therefrom. At a step 108, the resist ink is removed by the use of organic solvent, trichloroethylene. Then, at a step 110, orientating processing is done to orient the liquid crystal parallelly. In the orientating processing, polyimide solution is slushed by a spinner at 3500 rpm and thereafter the substrate is maintained at temperatures of 300.degree. C. for 30 minutes and 400.degree. C. for 30 minutes and fired thereby to form an orientation film on the conductive film. Then rubbing the orientation film is done by the use of chemical fiber cloth to provide orientation of liquid crystal filled in later. At a step 112, sealing material is printed on side portions by the use of epoxy resin. Further, at a step 114, glass fiber particles in particle diameter of 10 .mu. m are spread as spacers on the orientation film. At a step 116, a pair of glass substrates each being processed as abovedescribed are put one upon another in parallel and maintained under temperature of 100.degree. C. for 2 hours for bonding so that a liquid crystal cell is provided. At a step 118, a reflection film is vapor-deposited on the other end surface of one of the transparent glass substrates to form a mirror surface thereat. At a step 120, liquid crystal is filled in an inner space of the liquid crystal cell by a decompressed injection process. At a step 122, an injection opening is sealed with epoxy adhesive.
As described above, forming the mirror surface is done after the orientating process. This is for the reason that, if forming the mirror surface is done before the orientation process, the mirror surface formed beforehand might be hurt in later processes such as the orientating process, it might be hurt when the glass substrate is attached to holding jigs for the orientating process, for instance, and the mirror surface might become uneven. Therefore, forming the mirror surface must be done after the orientating process.
Here, it has been found experimentally that, when the liquid crystal cell obtained after the orientating process is heated to above 160.degree. C., the orientation is disturbed. This means that temperature of the substrate must be maintained below 160.degree. C. at least in the process of forming the mirror surface. In the case of forming the mirror surface of metals such as chrome, chromel of aluminumby vapor-depositing in a vacuum, however, it is generally considered to heat the substrate to temperature as high as 200.degree. C.-300.degree. C. so that adhesiveness of the metal film to the substrate is increased. Therefore, the abovedescribed metals cannot be used for forming the mirror surface in the case of the reflection mirror using the liquid crystal cell in which the mirror surface must be formed below temperature of 160.degree. C.